Fluid Mechanics is the study of fluids as an important branch of engineering mechanics. Almost everything on this planet either is a fluid or moves within or near a fluid. The essence of the subject of fluid flow is a judicious compromise between theory and experiment. This textbook not only makes a great deal of theoretical treatment available, but also provides experimental results as a natural and easy complement to the theory. The principles considered in the book are fundamental, and have been well established. However, in presenting this important subject, we have drawn on our own ideas and experience. Throughout the revisions, the informal and student-oriented writing style has been retained and further enhanced, and if it succeeds, has the flavor of an interactive lecture by the authors.